How does sea ice “bottle up” glaciers?
Sea ice is highly unstable and much softer than fresh water ice. In addition to that, there would be nothing to stop a glacier flow from pushing sea borne ice out of it’s way.
What stops most glacier movement is terrain. Mountain ranges are mostly responsible for holding Antarctica’s ice on the continent. There are a few ice flows where there are breaks in the mountainous terrain, so the ice flows to the ocean at those points.
This is wayyyy out of my field, but I looked it up, and apparently an ice shelf is very different from normal sea ice. An ice shelf is a glacier that has flowed out onto the water, and it is much stronger than sea ice and therefore CAN and does bottle up glacial ice on land behind it. If you can find someone who actually knows what he's talking about here, I'd defer to them.